Genomic DNA is a dynamic structure in mammalian cells. It undergoes sequence changes by cytosine methylation and by DNA recombinational rearrangements, deletions and amplifications. These dynamic alterations are important features of the normal programmed differentiation of cells and tissues during development and during aging, an extension of development in the adult. Unfortunately, this capacity for genomic restructuring also permits abnormal rearrangements, leading to precocious aging, lymphomas and leukemias and a variety of other cancers, especially when oncogenes are involved. This proposal aims to analyze the DNA restructuring which occurs as human genomes differentiate in the process of cell lineage and tissue development. Using a repetitive sequence probe (L2Hs) the restriction fragment length polymorphisms (RFLPs) between an individual's somatic tissue DNAs will be described by comparison to his gametic sperm DNA. (The L2Hs probe resolves such genomic differences and, therefor, permits the proposed experiments to be performed.) Employing blot hybridizations, recombinant DNA cloning and DNA sequencing, the types of genomic DNA differentiations which occur in development will be elucidated. Information will also be obtained on the types of sequences and possible recombinational mechanism(s) involved in this process. These studies will increase our understanding of the dynamic potential of human genomes for rearranging their genetic material. In addition to elucidating important details of developmental regulation and aging, this knowledge may provide basic information for resolving some of the aberrant recombinational processes which lead to disease.